The results summarized below were obtained in collaborative studies. Atropine inhibits cAMP-specific phosphodiesterase type 4 Atropine is a clinically useful muscarinic receptor antagonist. Interestingly, by using various biochemical and biophysical approaches, we found that atropine also functions as an allosteric phosphodiesterase type 4 (PDE4) inhibitor. This activity, which is independent of atropines ability to block muscarinic receptors, most likely contributes to the tachycardic and arrhythmogenic properties of this drug. (Perera RK, Fischer TH, Wagner M, Dewenter M, Vettel C, Bork NI, Maier LS, Conti M, Wess J, El-Armouche A, Hasenfu G, Nikolaev VO. Atropine augments cardiac contractility by inhibiting cAMP-specific phosphodiesterase type 4. Sci Rep 7, 15222, 2017) Modulation of basal ganglia function by the M4 muscarinic receptor Cholinergic regulation of dopaminergic inputs into the striatum is critical for normal basal ganglia function. This regulation is thought to be primarily mediated by acetylcholine released from cholinergic interneurons acting locally in the striatum. We found that extra-striatal cholinergic projections from the pedunculopontine nucleus to the substantia nigra pars reticulata act on M4 muscarinic receptors to counteract D1 dopamine receptor signaling in presynaptic terminals of direct pathway striatal spiny projections neurons. Activation of these M4 receptors induces a tonic inhibition of transmission at direct pathway synapses and D1 receptor-mediated activation of motor activity. These data provide novel insights into the role of M4 receptors in modulating striatal function. (Moehle MS, Pancani T, Byun N, Yohn SE, Wilson GH 3rd, Dickerson JW, Remke DH, Xiang Z, Niswender CM, Wess J, Jones CK, Lindsley CW, Rook JM, Conn PJ. Cholinergic projections to the substantia nigra pars reticulata inhibit dopamine modulation of basal ganglia through the M4 muscarinic receptor. Neuron 96, 1358-1372, 2017) Role of M4 muscarinic receptors expressed by cholinergic and D1 dopamine receptor-expressing neurons in regulating positive reinforcement and impulsivity Muscarinic receptors play important roles in reward learning and drug addiction. We found that mice lacking M4 receptors in D1 dopamine receptor-expressing neurons displayed greater cocaine-seeking and drug-primed reinstatement than their littermate controls in a Pavlovian conditioned place preference paradigm. Furthermore, these mutant mice initiated significantly more premature responses in the 5-choice-serial-reaction-time-task, indicative of impaired waiting impulse control. Interestingly, mice lacking M4 receptors in cholinergic neurons did not acquire cocaine Pavlovian conditioning and were unable to learn positive reinforcement to either natural reward or cocaine in an operant runway paradigm. This study illustrates that M4 receptors expressed by specific neural populations have different effects on learning processes related to both natural reward and drugs of abuse. (Klawonn AM, Wilhelms DB, Lindstrm SH, Singh AK, Jaarola M, Wess J, Fritz M, Engblom D. Muscarinic M4 receptors on cholinergic and dopamine D1 receptor-expressing neurons have opposing functionality for positive reinforcement and influence impulsivity. Front Mol Neurosci 11, 139. doi: 10.3389/fnmol.2018.00139, 2018) Cognition-enhancing and antipsychotic-like effects of a selective M4 receptor positive allosteric modulator Positive allosteric modulators (PAMs) targeting the M4 receptor are able to ameliorate the positive and cognitive symptoms in animal models of schizophrenia. We examined the effects of repeated dosing with a highly selective M4 receptor PAM (VU0467154) on either acquisition and/or consolidation of learning and memory when dosed alone or after pharmacologic challenge with the NMDA receptor antagonist MK-801. MK-801 challenge represents a frequently used preclinical model of NMDA receptor hypofunction, a characteristic feature of schizophrenia. We demonstrated that VU0467154 exerted long-term cognition-enhancing and antipsychotic-like effects without the development of tolerance, further corroborating the concept that M4 receptor PAMs may prove useful as novel therapeutic agents. (Gould RW, Grannan MD, Gunter BW, Ball J, Bubser M, Bridges TM, Wess J, Wood MW, Brandon NJ, Duggan ME, Niswender CM, Lindsley CW, Conn PJ, Jones CK. Cognitive enhancement and antipsychotic-like activity following repeated dosing with the selective M4 PAM VU0467154. Neuropharmacology 128, 492-502, 2018) M2 and M5 muscarinic receptors regulate bitter response of urethral brush cells Recent work has identified a cholinergic chemosensory cell type in the urethral epithelium (urethral brush cells = UBCs), that, upon stimulation with bitter substances, mediate a reflex detrusor activation. In this study, we found that M2 and M5 receptors attenuate the bitter response of UBCs via a cholinergic negative autocrine feedback mechanism. Cystometry studies suggested that dysfunction of certain muscarinic receptor subtypes, particularly of the M5 receptor, may lead to bladder overactivity. (Deckman K, Rafiq A, Erdmann C, Illig C, Durschnabel M, Wess J, Weidner W, Bschleipfer T, Kummer T. Muscarinic receptors 2 and 5 mediate a negative autocrine feedback mechanism in urethral brush cells activated by bitter stimuli. FASEB J 32, 2903-2910, 2018) M3 muscarinic receptor signaling prevents efficient remyelination by oligodendrocyte progenitor cells Muscarinic receptor antagonists act as potent inducers of oligodendrocyte differentiation and accelerate remyelination. However, the use of muscarinic antagonists in the clinic is limited by poor understanding of the operant receptor subtype, and questions regarding possible species differences between rodents and humans. By using a wide array of experimental approaches, we demonstrated that M3 receptors expressed by human oligodendrocyte progenitor cells act to delay differentiation and remyelination. For this reason, the M3 receptor represents an attractive target for induced remyelination in human disease. (Welliver RR, Polanco JJ, Seidman RA, Sinha AK, O'Bara MA, Khaku ZM, Santiago Gonzlez DA, Nishiyama A, Wess J, Feltri ML, Paez PM, Sim FJ. Muscarinic receptor M3R signaling prevents efficient remyelination by human and mouse oligodendrocyte progenitor cells. J Neurosci. 2018 1862-17, doi: 10.1523/JNEUROSCI.1862-17.2018; Epub ahead of print)